The water felting of dilute aqueous dispersions of mineral wool and lightweight aggregate is a well-known commercial process for manufacturing acoustical ceiling tiles. In this process, an aqueous slurry of component materials such as mineral wool, perlite, binder such as starch or latex, inorganic material and cellulosic fiber is deposited onto a moving foraminous support wire, such as a Fourdrinier or Oliver mat forming machine, for dewatering or drainage. The slurry may first be drained by gravity followed by vacuum suction to form a base mat. The wet base mat is then pressed to the desired thickness between rolls to remove additional water. The pressed base mat is then dried in ovens before the dried material is cut to the desired dimensions. The surfaces of the cut material can be sanded and coated on the top and or bottom to produce ceiling tiles and panels.
Ceiling tile used in suspended ceilings should have certain performance characteristics that include sound absorbing capacity, relatively low density, flame spread and optionally fire-resistance, and sag-resistance. Besides meeting these criteria, the raw materials need to be relatively inexpensive to procure and easy to process. These characteristics can be difficult to achieve even with a composite material. Moreover, the universe of available recycled materials that can contribute one or more of these desirable characteristics, that is compatible with other viable materials, that is available at a practical cost and that does not introduce undesirable characteristics is limited. It is important to find a formulation that achieves these essential characteristics, but also is compatible with existing manufacturing equipment and processes.
Mineral wool acoustical tiles are very porous which results in good sound absorption. U.S. Pat. Nos. 3,498,404; 5,013,405; 5,047,120 and 5,558,710 disclose mineral fillers may be incorporated into the composition to improve sound absorbing properties and to provide lightweight acoustical tiles and panels.
The acoustical tile compositions include a lightweight aggregate, typically expanded perlite. While the use of expanded perlite can require a high level of water to form a workable slurry, the use of high density perlite can alleviate this problem. U.S. Pat. No. 8,393,233 to Palm et al discloses employing expanded glass beads rather than perlite. Inorganic materials, such as clay may be used in ceiling tiles to impart fire resistance (as defined by ASTM Test Method E119) because the clay sinters during the fire endurance test. Various commercial clays such as kaolin, and bentonite, etc. can be used in ceiling tile fabrication. Gypsum is a useful inorganic material because it also acts as a flocculent. Calcium carbonate is another useful inorganic material because it is inexpensive and can add hardness to the finished product.
Mineral wool-based acoustical ceiling tile compositions must contain a binder. Starch is usually used as the binder in mineral wool-based ceiling tiles. U.S. Pat. Nos. 5,911,818 and 5,964,934 suggest as much as 15% by weight of the composition may be starch although about 6 or 7% by weight is conventionally used.
U.S. Pat. No. 6,855,753 to Englert discloses an acoustical tile composition in which the conventional starch binder is replaced by a wet-strength resin, such as a polyamine epichlorohydrin resin. This can be fabricated into ceiling tiles and panels using conventional water felting processes and equipment. The compositions, with the polyamine epichlorohydrin resins binder, can be dried significantly faster than comparable compositions containing conventional starch binders.
U.S. Pat. No. 7,056,582 to Carbo et al discloses a composition for a slurry for manufacture of acoustical panels includes one or more fillers, one or more binders, water and zinc pyrithione. At least one of the fillers and/or binders includes microbial nutrients in an amount of at least 1% based on the dry weight of the acoustical panel. In another embodiment of the invention, acoustical panels include a core having a plurality of opposing surfaces and being at least ⅛ inches thick. The core comprises the dried product of a slurry of fillers, binders and water. Zinc pyrithione is present in at least one of the core and a coating applied to at least one of the surfaces of the core.
U.S. Pat. No. 8,057,915 to Song et al discloses an acoustical product including a matrix of calcium sulfate dihydrate crystals and expanded perlite distributed throughout the matrix. The expanded perlite has a particle size distribution with at least 10% of the perlite having a particle diameter of 700 microns or more, and the amount of expanded perlite to calcium sulfate dihydrate is about 35% to about 75% by weight, based upon the dry weight of the calcium sulfate dihydrate. A dispersing agent and glass fibers having a particle length of about ¼ inch to about 1 inch are dispersed throughout the gypsum matrix.
U.S. Pat. No. 8,133,354 to Baig discloses a composition and process suitable for making acoustical tiles. Certain embodiments of the composition comprise: perlite; an inorganic material selected from the group consisting of calcium sulfate, calcium carbonate, clay and mixtures thereof; a binder selected from the group consisting of starch, a combination of starch and cellulosic fibers, latex, kraft paper gel and mixtures thereof; optionally mineral wool; optionally gypsum; and cellulosic fiber, wherein at least a portion of the cellulosic fiber and at least a portion of the inorganic material are pulp and paper processing waste comprising cellulosic fiber, clay and calcium carbonate. Certain embodiments of the process comprise: forming an aqueous slurry; continuously flowing slurry onto a moving foraminous wire to form a cake; dewatering the cake to form a base mat; and drying the base mat.
U.S. Pat. No. 8,383,233 to Palm et al discloses a water felted base mat for a suspended ceiling tile comprising on a weight basis about ½ mineral wool, starch binder, limited to about ⅛, newsprint, limited to about ⅛, and about ¼ expanded glass beads.
The cellulosic fiber for ceiling tiles in compositions and methods of the present invention is obtained from newsprint being recycled. Typically, either hammer-milled and/or hydropulped newsprint being recycled is employed as the cellulosic fibers.